1. Field of the Invention
The present invention relates to machine shop apparatus for shaping and forming sheet metal, and more particularly to a holder for the punch of a press brake.
2. Description of the Related Art
Most sheet metal machine shops are commonly equipped with a press brake for shaping and forming sheet metal. The press braise is used to form flanges and other bends and shapes in long or thin strips of sheet metal. The device generally includes a frame which has a long apron supporting a press table or bed on which is mounted a female die or molding. Vertically above the press table is another apron, often referred to as a ram, on which is mounted a male die or punch. Although in some presses the lower apron, or both aprons, are moveable, more commonly the ram is slidably moved in the vertical direction with great force against the stationary press table in order to compress the work piece between the punch and the female die, thereby bending and shaping the sheet metal according to the particular punch and die combination. The ram may be operated by a pair of hydraulic cylinder and piston assemblies at either end of the ram, or by a mechanical crankshaft. Usually the apparatus will include a flywheel to maintain sufficient energy to operate the ram, the flywheel maintaining the energy level at idle when the ram is not in use.
The ram and the press table are often quite long, press brakes between seven feet and twenty feet not being uncommon. The punch and the die are removable and replaceable assemblies, there being different designs of punches to impart different shapes to the metal. The punch may be one long continuous piece, or the punch may be shorter, discrete pieces attached end to end along the length of the ram. Various problems may result from this construction.
For precision work, it is desirable to form bends or shapes which are uniform in depth throughout the length of the work piece. Since the pistons exert the greatest force at the ends of the ram, over a period of time the ram or die may develop a curvature towards the center due to constant wear, or other irregularities my develop on the surface of the punch or the press table.. Consequently, it is desirable to provide some means for adjusting the depth or curvature of the punch. Further, the punch must be clamped to the ram, the clamps usually being secured by bolts. It has been found that better clamping action is obtained by using a plurality of clamps along the length of the ram than a single long clamp. With a plurality of discrete clamps attached along the length of the ram, it is inconvenient, time consuming, and inefficient to have to unbolt and bolt each clamp individually when replacing the punch. A central mechanism for controlling and releasing the clamps quickly is therefore desirable.
A variety of devices have been developed for addressing these problems. U.S. Pat. No. 4,354,374, issued Oct. 19, 1982 to H. Deguchi, teaches a punch mounted on a slide and a die mounted on a press table, where pairs of wedges are installed under the table, the top wedge being attached to the table and the bottom wedge being slidable. The bottom has a rack engaged by a pinion operable from the front of the table, such that as the rack is adjusted, the wedges raise and lower the height of the table in order to control the depth of the cut. U.S. Pat. No. 4,733,552, issued Mar. 29, 1988 to M. Leflis, shows a press with relocatable dies at fixed work stations for performing multiple shaping operations on strip fed sheet metal.
U.S. Pat. No. 4,787,237, issued Nov. 29, 1988 to Houston, et al., describes clamps for holding the punch and the die, the clamps having a fixed member and an L-shaped member slidable on a bolt connecting the fixed and slidable members. A pneumatically or hydraulically operated cylinder and piston are mounted concentrically with the bolt adjacent the fixed member, a spring biasing the piston to extend from the cylinder against the fixed member to pull the slidable member to a clamping position, the application of air or hydraulic pressure causing the piston to retract so that the slidable member relaxes to an open position. U.S. Pat. No. 4,895,014, issued Jan. 23, 1990 to D. L. Houston, shows an improvement in the foregoing clamp system having segmented clamps with one embodiment in which the clamp is released mechanically by rotating a cammed handle which moves a row of wedges longitudinally down the length of the ram or press table, moving the clamps laterally to a release position overcoming the bias of the springs, and a second embodiment in which pneumatic or hydraulic pressure forces a piston against an elongated clamp contact member which moves the individual clamp segments.
U.S. Pat. No. 5,009,098, issued Apr. 23, 1991 to J. L. Merksteijn, describes a press having curve forming means to compensate for sagging in the bends produced in the work piece resulting from wear or irregularities in the punch or die, consisting of strips with members moveable longitudinally and transversely with each other, which shim the table, being angled more in the center than at the ends, and being moveable longitudinally by a hand crank or electrical or hydraulic means. U.S. Pat. No. 5,022,256, issued Jun. 11, 1991 to J. van der Meulen, shows a clamping device having a fixed jaw and a pivoting jaw with a resilient strip between the two, the resilient strip having a wedge which interlocks with the punch tool. A hydraulic cylinder pushes a piston against the pivoting jaw to clamp the tool.
U.S. Pat. No. 5,065,610, issued Nov. 19, 1991 to K. Yonezawa, teaches a clamp having a front jaw and a back jaw, the front jaw being separated into separate plates longitudinally, the clamp being spring biased to normally hold the clamp. The clamp is released by hydraulic pressure, each plate having a cylinder and piston, the pistons extending to push the jaw away from the punch, the cylinders being connected by a continuous hydraulic line with pipes between the individual plates. U.S. Pat. No. 5,113,686, issued May 19, 1992 to T. Kawahara, shows a pin for precisely locating the die on a "bolster". The pin is placed in registered recesses in the die and the bolster and has resilient collars which expand when the collar is pressed in the die.
U.S. Pat. No. 5,121,626, issued Jun. 16, 1992 to J. B. Baldwin, shows a means for clamping a die to the ram or the bed which has an adjustment means to counteract wear on the die. The device includes a support bracket with an angled lower surface, a thrust member having a wedge shape under the bracket's lower surface, and a disk rotatably mounted on the bracket which engages a slot on the thrust member in order to move the thrust member laterally to raise and lower the die. U.S. Pat. No. 5,460,027, issued Oct. 24, 1995 to Y. Takahashi, shows a clamp for attaching punches with a uniformly planar shank or punches with a longitudinal groove in the shank for engaging a projection on the clamp. The clamp is attached to the ram by bolts and has a lower projection for engaging a groove on the shank, the projection being pivotal and spring biased against the shank of the punch.
A series of patents have been issued to S. Kawano, including U.S. Pat. Nos. 5,390,527, issued Feb. 21, 1995; 5,507,170, issued Apr. 16, 1996; 5,511,407, issued Apr. 30, 1996; 5,513,514, issued May 7, 1996; 5,572,902, issued Nov. 12, 1996; 5,619,885, issued Apr. 15, 1997; 5,642,642, issued Jul. 1, 1997; and 5,685,191, issued Nov. 11, 1997. U.S. Pat. No. 5,794,486, issued Aug. 18, 1998 to Sugimoto, et al., describes another variation on the Kawano devices.
The Kawano patents show a clamp mounted on a holder operated by a lever rotating between stops, the punch being held between the clamp and the holder, a wedge between the holder and the ram, the clamp being resiliently biased against the holder. Variations include a triangular wedge between the clamp and the punch, the wedge having a projection engaging a groove on the shank of the punch, the triangular wedge being spring biased, hydraulic cylinders to release the clamp, mating projections on the clamp and punch to prevent the punch from accidentally falling, an adjustable clamp piece mounted on the clamp pushing against a spring or elastic member, an elastic clamp, etc.
German Patent No. 616,783, published Aug. 5, 1935, describes an adjustment mechanism mounted on the ram for counteracting curvature of the ram or the bed, which includes a lower wedge strip extending the length of the ram, and a pair of upper wedge strips divided at the center of the ram, the slope of the wedges diminishing from the center of the rams to the ends, the curvature of the punch being adjusted by attaching the ends of the wedge strips to adjustment screw spindles at the ends of the ram, the screws pulling the upper wedge strip over the lower wedge strip to form a gap in the center, the angles of the wedges increasing the depth of the punch towards the center of the ram.
The present invention deals only with the problem of alleviating the time and inconvenience involved in unbolting a plurality of clamps to release the punch. It does not purport to address the problem of wear and irregularities in the punch or die.
The three newest clamp holding devices available include the Wilson Express Clamp, made by Wilson Tool International, the Amada One Touch (see the Kawano patents cited above), and a system made by MachineFabrik Wila. The Wilson and Amada devices employ a rotary handle to release each clamp. While this represents an advance over past systems which required unbolting two bolts per clamp with perhaps thirty to forty clamps over a ten foot length of ram, nevertheless it still leaves the problem of operating thirty to forty rotary handles over a ten foot length of ram. The Wila device employs a hydraulic bladder type apparatus to release the clamps. The problem with this device is that the hydraulic system is complicated, expensive, and may develop a leak, rendering the system inoperable. Further, since the hydraulic lines are continuous, the Wila system precludes the flexibility of selectively removing individual punches normally permitted in manual systems.
Therefore, there is a need for a mechanical device which will open a plurality of clamps simultaneously to release to release the punch. None of the above inventions and patents, taken either singularly or in combination, is seen to describe the instant invention as claimed. Thus a press brake punch holder solving the aforementioned problems is desired.